(1.) Field of the Invention
The present invention relates to a printing apparatus, and more particularly to a printing apparatus in which image data is transmitted from a printer control unit to an engine control unit in units of bands.
(2.) Description of the Related Art
Generally, an existing printing apparatus, such as an ink-jet printer or a laser beam printer, receives print data sent by a host computer, converts the print data into image data, and transmits the image data to a printing control unit. The printing control unit controls scanning of a printing head based on the received image data so that the printing head prints an image of the image data.
In order to transmit print data from the host computer to the printing apparatus, several printer interfaces are commonly used. The printer interfaces fall into two broad categories. In one of the broad categories, raster and other processing of an image to be printed are performed by the host computer, and the print data as a result of the raster processing is transmitted. In the other broad category, print data and a print command are transmitted to the printing apparatus by the host computer, and raster and other processing of the print data are performed by the printing apparatus in response to the print command.
For example, Centronics interface belongs to the former category. In a case of Centronics interface, the host computer creates image data by performing raster processing of an image using a printer driver provided in the host computer. The image data is transmitted to the printing apparatus by the host computer through the Centronics interface. The raster and other processing of an image to be printed are performed by the host computer, and it is not necessary for the printing apparatus to have a high-performance microcomputer. The printer interface of this category is effective in providing a low-cost printing apparatus.
However, in the case of the former category, the speed of printing by the printing apparatus depends on the speed of processing by the host computer, and it takes a long time to transmit the image from the host computer to the printing apparatus even if a high-performance microcomputer is contained in the host computer. The printer interface of this category provides the printing apparatus with a relatively low printing speed.
In a case of the latter category, the print data and the print command are transmitted to the printing apparatus by the host computer. It takes little time to transmit the print data from the host computer to the printing apparatus. The printer interface of this category is effective in providing a printing apparatus having a relatively high printing speed.
However, in the case of the latter category, it is necessary that the printing apparatus be provided with a page buffer in which the print data sent by the host computer is stored. In the printing apparatus, the raster and other processing of the stored print data must be performed in response to the print command. In order to carry this out, it is necessary that the printing apparatus be constructed by a high-performance microcomputer and a page buffer having a large capacity of storage.
In recent developments, a display-list method has been proposed as a new method of transmitting print data from the host computer to the printing apparatus. According to the display-list method, a unit data of the print data transmitted by the host computer to the printing apparatus is defined as a band. In the host computer, print data is divided into a plurality of bands, and a print command is generated for a respective one of the plurality of bands of the print data. A respective one of the plurality of bands and a related print command generated therefor are transmitted to the printing apparatus by the host computer. In the printing apparatus, the raster and other processing of the received image data are performed in response to the print command with respect to each of the plurality of bands.
If a printing apparatus were to be suitably adapted to the display-list method mentioned above, the printing apparatus would provide a higher speed of transmission of image data than the speed of transmission of image data in the case of the conventional Centronics interface. Further, if a printing apparatus could take full advantage of the display-list method, it would not be necessary that the printing apparatus be provided with a page buffer having a large capacity of storage as in the case of the conventional command-based printer interface. The use of the display-list method would be more effective in providing a low-cost printing apparatus than the use of the conventional command-based printer interface.
However, the existing printing apparatus is not suitably adapted to the display-list method. It is difficult for the existing printing apparatus to efficiently process the image data sent by the host computer in units of bands in accordance with the display-list method.